U.S. patent application number 15/764064 was filed with the patent office on 2018-11-01 for fabrication of optical interconnect structures for a photonic integrated circuit.
The applicant listed for this patent is Arizona Board of Regents on Behalf of the University of Arizona. Invention is credited to THOMAS L. KOCH, ROBERT A. NORWOOD, STANLEY K. H. PAU, Nasser N. PEYGHAMBARIAN.
Application Number | 20180314151 15/764064 |
Document ID | / |
Family ID | 58424844 |
Filed Date | 2018-11-01 |
United States Patent
Application |
20180314151 |
Kind Code |
A1 |
KOCH; THOMAS L. ; et
al. |
November 1, 2018 |
FABRICATION OF OPTICAL INTERCONNECT STRUCTURES FOR A PHOTONIC
INTEGRATED CIRCUIT
Abstract
A method of fabricating an optical connection to at least one
planar optical waveguide integrated on a planar integrated circuit
(PIC) uses a machine vision system or the like to detect one or
more positions at which one or more optical connections are to be
made to at least one planar optical waveguide located on the PIC. A
spatial light modulator (SLM) is used as a programmable
photolithographic mask through which the optical connections are
written in a volume of photosensitive material using a
photolithographic process. The SLM is programmed to expose the
photosensitive material to an illumination pattern that defines the
optical connections. The programming is based at least in part on
the positions that have been detected by the vision system. The
optical connections are printed by exposing the photosensitive
material to illumination that is modulated by the pattern with
which the SLM is programmed.
Inventors: |
KOCH; THOMAS L.; (TUCSON,
AZ) ; NORWOOD; ROBERT A.; (TUCSON, AZ) ; PAU;
STANLEY K. H.; (TUCSON, AZ) ; PEYGHAMBARIAN; Nasser
N.; (TUCSON, AZ) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Arizona Board of Regents on Behalf of the University of
Arizona |
Tucson |
AZ |
US |
|
|
Family ID: |
58424844 |
Appl. No.: |
15/764064 |
Filed: |
October 3, 2016 |
PCT Filed: |
October 3, 2016 |
PCT NO: |
PCT/US2016/055199 |
371 Date: |
March 28, 2018 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
62236445 |
Oct 2, 2015 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G03F 7/027 20130101;
B29D 11/00 20130101; G03F 7/2057 20130101; B29D 11/0075 20130101;
G03F 7/038 20130101; G03F 7/0037 20130101; G03F 7/0005 20130101;
G02B 6/1228 20130101; G02B 6/12004 20130101; G02B 6/124 20130101;
G03F 7/0757 20130101 |
International
Class: |
G03F 7/00 20060101
G03F007/00; G03F 7/20 20060101 G03F007/20; B29D 11/00 20060101
B29D011/00; G02B 6/124 20060101 G02B006/124; G02B 6/122 20060101
G02B006/122; G02B 6/12 20060101 G02B006/12 |
Claims
1. A method of fabricating an optical connection to at least one
planar optical waveguide integrated on a planar integrated circuit
(PIC), comprising: detecting one or more positions at which one or
more optical connections to the at least one planar optical
waveguide are to be formed; configuring a spatial light modulator
(SLM) for use as a programmable photolithographic mask through
which the one or more optical connections are able to be written in
a volume of photosensitive material using a photolithographic
process, the configuring including programming the SLM to expose
the volume of photosensitive material to an illumination pattern
that defines the one or more optical connections, the programming
being based at least in part on the detected positions; and
printing the one or more optical connections in the volume of
photosensitive material by exposing the volume of photosensitive
material to illumination that is modulated by the pattern with
which the SLM is programmed.
2. The method of claim 1, further comprising simultaneously
printing a plurality of optical connections by programming the SLM
to expose the volume of photosensitive material to an illumination
pattern that defines the plurality of optical connections.
3. The method of claim 1, further comprising: monitoring the
printing using a vision measuring system to obtain location
information; based on the location information, adjusting the
programming of the SLM while printing is in progress.
4. The method of claim 3, wherein adjusting the programming of the
SLM includes adjusting the programming of the SLM to reduce optical
loss in the one or more optical connections being printed.
5. The method of claim 1, wherein the at least one optical
connection includes an optical waveguide.
6. The method of claim 1, wherein programming the SLM based at
least in part on the detected positions includes calculating at
least starting and ending locations and a dimension of the one or
more optical connections that are to be printed.
7. The method of claim 1, wherein the photosensitive material
includes a photopolymer.
8. The method of claim 1, wherein printing the one or more optical
connections comprises a plurality of different exposures that each
print a portion of the one or more optical connections.
9. The method of claim 8, wherein one or more optical connections
includes a three-dimensional (3D) optical structure and the
different exposures each form a two-dimensional (2D) layer portion
of the 3D optical structure.
10. The method of claim 1, wherein detecting the one or more
positions further comprises detecting any obstructions on the PIC
that are to be avoided when printing the one or more optical
connections.
11. The method of claim 3, wherein printing the one or more optical
connections comprises a plurality of different exposures that each
print a portion of the one or more optical connections and further
wherein monitoring the printing includes using the vision measuring
system to detect defects arising in one exposure step before
proceeding to another exposure step.
12. A method of fabricating an optical connection between first and
second optical elements located on one or more planar integrated
circuits (PICs), comprising: arranging first and second diffractive
optical elements on the one or more PICs; launching, from a
direction out of a plane in which the PIC extends, first and second
photolithographic write beams into the first and second diffractive
optical arrangements, respectively, such that the write beams are
re-directed into the plane in which the one or more PICs extend and
into a photosensitive volume of material so that interference
arising between the two write beams causes the optical connection
to be written in the photosensitive volume of material.
13. The method of claim 12, wherein at least one of the PICs
includes a planar optical waveguide in which the first diffractive
optical element is integrated so that the optical connection is
optically self-aligned with the planar optical waveguide upon being
written.
14. The method of claim 13, wherein the planar optical waveguide
has a tapered portion that traverses the first diffractive optical
element.
15. The method of claim 13, wherein at least one of the first and
second diffractive optical elements includes a grating coupler.
16. The method of claim 15, wherein the grating coupler is
configured to couple optical wavelengths that are out-of-band with
respect to optical wavelengths that propagate in the planar optical
waveguide.
17. The method of claim 1, wherein the photosensitive material is
selected from the group consisting of polysiloxane, acrylate, SU-8
and sol-gel.
18. The method of claim 1, wherein the photosensitive material
includes a photopolymer.
19. A method of optically coupling first and second planar optical
waveguides that are laterally misaligned with respect to one
another, comprising: positioning a first planar optical waveguide
in contact to a second planar optical waveguide, said second
waveguide having an end portion with an inverse taper, arranged so
that the first waveguide is longitudinally positioned and in
contact along a length of an end portion of the taper in the second
waveguide so that adiabatic optical coupling occurs from between
the first and second waveguides, the adiabatic coupling being
achieved even when first and second waveguides are laterally
misaligned by a distance comparable to a core dimension of the
first waveguide.
20. A method of optically coupling first and second planar optical
waveguides that are laterally misaligned with respect to one
another, comprising: positioning a first planar optical waveguide
having a first end portion with an end taper so that it is
optically coupleable to a second planar optical waveguide having a
second end portion with an inverse taper, the first and second end
portions being laterally misaligned with respect to one another;
and printing an optical connection in a volume of photosensitive
material in accordance with a photolithographic process, the
optical connection optically coupling the first planar optical
waveguide to the second planar optical waveguide, alignment between
the optical connection and the first planar optical waveguide being
laterally offset by a first amount and an alignment between the
optical connection and the second planar optical waveguide being
laterally offset by a second amount that is different from the
first amount.
21. One or more optical connections fabricated in accordance with
the method of claim 1.
22. One or more optical connections fabricated in accordance with
the method of claim 12.
23. One or more optical connections fabricated in accordance with
the method of claim 20.
24. One or more planar integrated circuits (PICs), comprising:
first and second diffractive optical elements integrated on the one
or more PICs; and a photopolymerized optical connection located in
a volume of photopolymer material volume, the photopolymerized
optical connection being self-aligned with the first and second
diffractive optical elements upon being written by launching, from
a direction out of a plane in which the PIC extends, first and
second photolithographic write beams into the first and second
diffractive optical arrangements, respectively, such that the write
beams are re-directed into the plane in which the one or more PICs
extend and into the volume of photopolymer material so that
interference arising between the two write beams causes the
photopolymerized optical connection to be written in the volume of
photopolymer material.
25. The one or more PICs of claim 24, wherein at least one of the
PICs includes a planar optical waveguide in which the first
diffractive optical element is integrated so that the
photopolymerized optical connection is optically self-aligned with
the planar optical waveguide upon being written.
26. The one or more PICs method of claim 25, wherein the planar
optical waveguide has a tapered portion that traverses the first
diffractive optical element.
27. The one or more PICs of claim 24, wherein at least one of the
first and second diffractive optical elements includes a grating
coupler.
28. The one or more PICs of claim 25, wherein at least one of the
first and second diffractive optical elements includes a grating
coupler.
29. The one or more PICs of claim 28, wherein the grating coupler
is configured to couple optical wavelengths that are out-of-band
with respect to optical wavelengths that propagate in the planar
optical waveguide.
30. A method of fabricating one or more optical interconnections to
at least one planar optical waveguide integrated on a planar
integrated circuit (PIC), comprising: using a vision system to
obtain location information specifying locations at which one or
more optical interconnections are to be printed on the PIC;
determining one or more write parameters that are to be used to
print an optical interconnect pattern that defines the one or more
optical interconnections, the one or more write parameters being
based at least in part on the location information obtained by the
vision system; and printing the one or more optical
interconnections in a volume of photosensitive material located on
the PIC in accordance with the write parameters.
31. The method of claim 30, wherein printing the one or more
optical interconnections includes printing the one or more optical
interconnections using a photolithographic process, the write
parameters including parameters that define an illumination pattern
that is to be projected onto the volume of photosensitive
material.
32. The method of claim 30, wherein printing the one or more
optical interconnections includes printing the one or more optical
interconnections with a 3D printer.
33. The method of claim 30, wherein printing the one or more
optical interconnections includes printing the one or more optical
interconnections with a scanning laser.
34. A method of fabricating one or more structures on a substrate,
comprising: detecting one or more positions at which one or more
structures are to be formed on the substrate; configuring a spatial
light modulator (SLM) for use as a programmable photolithographic
mask through which the one or more structures are able to be
written in a volume of photosensitive material using a
photolithographic process, the configuring including programming
the SLM to expose the volume of photosensitive material to an
illumination pattern that defines the one or more structures, the
programming being based at least in part on the detected positions;
and printing the one or more structures in the volume of
photosensitive material by exposing the volume of photosensitive
material to illumination that is modulated by the pattern with
which the SLM is programmed.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of U.S. Provisional
Application Ser. No. 62/236,445, filed Oct. 2, 2015, the entire
contents of which are incorporated herein by reference.
BACKGROUND
[0002] An important problem in optical packaging involves the
optical interconnection of planar-integrated photonic integrated
circuits (chip-chip connections) and the connection of such
circuits to optical fibers (fiber-chip connection). Photonic
Integrated Circuits (PICs) refer to waveguide-based photonic
components, including optical integrated devices such as lasers,
optical amplifiers, switches, filters, modulators, splitters and
the like; PICs can also include integration with semiconductor
devices such as CMOS devices. PICs allow systems with high
complexity and multiple functions to be integrated on a single
substrate to thereby allow the generation, detection, propagation
and modulation of both optical and electrical signals. PICs may
employ a variety of different material systems, including silicon,
silicon dioxide, polymer, lithium niobate, InP and GaAs, and
optical interconnection processes should be compatible with these
material systems. Existing wire bonding techniques that have been
successfully applied to electrical connections in electronic
integrated circuits cannot be easily extended to optical connection
in a photonic integrated circuit.
[0003] The components of a PIC are generally manufactured by
different processes and the dimensions of the components have
different specifications and variations. For example, the variation
in the dimensions of a CMOS detector is determined by extreme
ultraviolet EUV lithography and is generally much less than a
micron. On the other hand, the variation in the dimensions of a
lithium niobate modulator fabricated by contact UV lithography can
be on the order of a micron. The different components are arranged
by a pick-and-place machine, for example, on a substrate to form a
final device. The dimensions and locations of the components can
fluctuate from one device to another. In order to form a single
mode optical connection between the components, the optical
connection must be positioned to within a fraction of a wavelength,
.lamda..sub.o/n, where .lamda..sub.o is the operating wavelength of
the optical connection and n is the refractive index. The
fabrication of many optical connections requires an active, robust
and expensive technique that takes into account the tolerances and
variation of the PIC configurations.
SUMMARY
[0004] In accordance with one aspect of the present disclosure, an
inexpensive, high-thoughput, relaxed tolerance method is presented
for fabricating interconnects on a Photonic Integrated Circuit
(PIC). In one particular, implementation, a machine vision system
or the like is used to detect one or more positions at which one or
more optical connections are to be made to at least one planar
optical waveguide located on the PIC. A spatial light modulator
(SLM) is configured for use as a programmable photolithographic
mask through which the one or more optical connections are able to
be written in a volume of photosensitive material using a
photolithographic process. The SLM is configured by programming the
SLM to expose the volume of photosensitive material to an
illumination pattern that defines the one or more optical
connections. The programming is based at least in part on the
positions that have been detected by the vision system. The one or
more optical connections are printed in the volume of
photosensitive material by exposing the volume of photosensitive
material to illumination that is modulated by the pattern with
which the SLM is programmed.
[0005] The use of the vision system to determine the positions at
which the optical connections are to be made on the PIC
advantageously avoids the need for use of a high precision
positioning stage to carefully align the PIC with the
photolithographic or other write system. Moreover, lateral
misalignments between the components on the PIC that are being
interconnected can be easily accommodated since the vision system
can determine and adjust the illumination pattern as needed for any
particular arrangement and placement of components
[0006] This Summary is provided to introduce a selection of
concepts in a simplified form that are further described below in
the Detailed Description. This Summary is not intended to identify
key features or essential features of the claimed subject matter,
nor is it intended to be used as an aid in determining the scope of
the claimed subject matter.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 shows a perspective view of one example of a Photonic
Integrated Circuit (PIC) to which the techniques described herein
may be applied.
[0008] FIGS. 2a and 2b show a simplified plan view and side-view,
respectively of a PIC that includes two chips.
[0009] FIG. 3 shows a cross-sectional view of the PIC shown in
FIGS. 2a and 2b taken along line A-A in FIG. 2a.
[0010] FIG. 4 is a block diagram view of an illustrative maskless
lithography system.
[0011] FIG. 5 is a flowchart illustrating one example of a
lithographic fabrication process.
[0012] FIG. 6 shows a simplified plan view of a PIC similar to that
shown in FIG. 2a in which an out-of-band writing technique is used
to fabricate an optical interconnect structure such as a
waveguide.
DETAILED DESCRIPTION
[0013] FIG. 1 shows a perspective view of one example of a Photonic
Integrated Circuit (PIC) to which the techniques described herein
may be applied. PIC 100 includes multiple photonic systems that are
integrated on different substrates ("chips") 2, 3 and 4 and which
contain lateral single-mode waveguides 50. The waveguides 50
positioned on different chips are to be interconnected and/or are
to be connected to input/output waveguide 6. The various components
2, 3 and 4 are mounted on a substrate 10 that serves as a component
carrier. The components of the PIC 100 are to be interconnected
with optical interconnect structures at connecting points 15, 16,
17 and 18. For instance, one optical interconnect structure may
interconnect points 15 and 16 and another optical interconnect
structure may interconnect points 17 and 18.
[0014] Fabrication of the optical interconnect structures will be
described with reference to FIGS. 2a and 2b, which show a
simplified plan view and side-view, respectively of a PIC 200 that
includes two chips 210 and 220 that are located on a substrate 230.
The chips 210 and 220 include respective waveguides 212 and 222
that are to be interconnected with one another. The waveguides 212
and 222 are generally (but not necessarily) silicon on insulator
(SOI) waveguide and may be formed, for example, on respective oxide
layers 215 and 217 that overlie chips 210 and 220, respectively.
The waveguides 212 and 222 include inverse tapers in which the
waveguide cross-section is decreased to a size that is typically
smaller than a maximum waveguide cross-section such that the
waveguide remains single mode, in order to also expand the mode
profile. In some embodiments the inverse tapers are adiabatically
tapered to allow optical energy to be adiabatically coupled with
minimal loss. The waveguides 212 and 222 are shown as being
misaligned and offset from one another. This misalignment may
result from less than optimal placement of the chips 210 and 220 on
the substrate 230.
[0015] In one embodiment, the interconnect structure is formed by a
photolithographic process. The process begins by applying a
photosensitive polymer 240 over at least the portions of the PIC
200 where the optical waveguide interconnect structures are to be
formed. In the example shown in FIG. 2 the polymer is applied as a
tape. In other implementations the polymer may be applied over the
structure as a fluid. In one embodiment a maskless lithographic
process may be used to induce polymerization reactions in the
polymer through photochemical processes. In this way the refractive
index of the exposed portions of the polymer material is increased
(or decreased) and an optical waveguide interconnect structure is
thus generated which is embedded in the polymer material. This can
also occur through a multi-photon process, whereby the wavelength
of the exposure is a multiple of the wavelength of the normal UV
radiation process. Whether the refractive index of the exposed
portions of the polymer material is increased or decreased depends
on the nature of the polymer that is used. In some cases the
exposed portions will increase the refractive index, in which case
the polymerization process will create the waveguide core. In other
cases the exposed portions will decrease the refractive index, in
which case the polymerization process will create the cladding
adjacent to the core.
[0016] It should be noted that while the example described herein
employs a selective photopolymerization process, other types of
reactions may be used to create refractive index changes in
polymers, such as by photodegradation and photoisomerization, for
instance.
[0017] By way of illustration, Table 1 shows several classes of
commercially available photopolymers that may be employed. In
addition to the classes shown, other varieties are available with
lower refractive indices and insertion losses. It should be noted,
however, that ultra-low propagation loss is generally not needed
for chip-to-chip interconnection applications.
TABLE-US-00001 TABLE 1 Loss @ 1550 nm Supplier and Polymer R.I.
range (dB/cm) comments ZPU12-RI 1.45-1.47 0.35 dB/cm ChemOptics
Photodefinable Wet and dry etchable VOAs in Korean Telecom ZPU13-RI
1.43-1.45 0.35 dB/cm ChemOptics Photodefinable Wet and dry etchable
VOAs in Korean Telecoms OE 4140 and 1.51-1.53 0.7 dB/cm Dow Corning
OE 4141 Photodefinable Similar mils used by IBM
[0018] Referring again to FIGS. 2a and 2b, the resulting optical
waveguide interconnect 260 formed in the polymer 240 can be
operated as a waveguide(s) with the ambient air functioning as
cladding material. However, the interconnect structures may also be
embedded in low-refractive cladding 250 and in this way can be
stabilized mechanically and protected against physical and chemical
environmental influences. In addition to allowing optical coupling
between waveguides in the vertical direction, the use of adiabatic
tapered waveguides as shown in this example advantageously enables
optical coupling between laterally offset waveguide as well. In
this way asymmetries that arise from misalignment can be
accommodated during the process of fabricating the interconnect
structure.
[0019] FIG. 3 shows a cross-sectional view of the resulting PIC 200
taken along line A-A in FIG. 2a. As shown, the lithographic process
described above defines the high index polymer portion 260 of
polymer 240 that is surrounded by low index polymer portions 242
and 244 of polymer 240. In some embodiments the polymer 240,
regardless of whether it is applied as a tape or in some other
form, may include two layers with different refractive indices,
with one layer serving as a core layer and the other layer serving
as a cladding layer. In the case of a tape, one of the layers may
be an adhesion layer to improve attachment. In this way the
multilayer polymer 240 is able to vertically confine optical energy
and the subsequent fabrication steps used to form the optical
interconnect structure only need to further define the multilayer
polymer 240 so that it laterally confines the optical energy along
the desired path.
[0020] While the optical interconnect structures that are formed
will typically be waveguides as illustrated above, more generally
the optical interconnect structures may be any structures having
regions where the refractive index is made to vary through
selective photopolymerization or other processes.
[0021] In one particular embodiment, a maskless lithographic
process that employs a spatial light modulator (SLM) is used to
form the optical interconnect structure. Low-cost SLM lithography
systems are available, for instance, with a mercury lamp source
offering a spatial resolution of 0.6 .mu.m for single exposure high
density waveguide fabrication. One example of such a system is
commercially available from Heidelberg Instruments.
[0022] FIG. 4 is a block diagram view of an illustrative maskless
lithography system 300. The maskless lithography system 300
includes a light source 310 such as the aforementioned mercury lamp
source or ultraviolet laser. The light from the light source 310 is
directed to a programmable SLM 320. The programmable SLM 320 is
configured to receive image pattern data, also referred to as mask
layout data, representative of a desirable lithographic pattern,
and direct light representative of the image to an optical
projection arrangement 330. The light from the optical projection
arrangement 330 then falls onto a photosensitive surface 380 of a
substrate 370. The optical projection arrangement 330 reduces the
dimensions of the image received from the programmable SLM 320 and
projects the reduced image onto the photosensitive surface of the
substrate.
[0023] The lithography system 300 also includes a control system
350 and a vision system 340 to measure the locations on the
substrate 370 at which the interconnections are to be made. The
vision system 340 may be, by way of illustration, a machine vision
camera, a microscope with scanning and stitching capabilities, an
x-ray inspection system, or a scanning electron microscope. The
control system 350 includes a computer processor, a memory, and a
user interface configured to enable a user to input data for
instructing the system 300 to produce a printed pattern on or in
the photosensitive surface of the substrate 370 on which the
optical interconnect structure is to be formed. The entire
lithographic system 300 is mounted on a scanning stage or robotic
arm 360 whose movement over the substrate is determined by the
control system 350 using information obtained from the vision
system 350.
[0024] The vision system 340 is used to precisely measure the
locations of the starting and ending points of the various optical
interconnects to be formed. The control system 350 processes the
information from the vision system 340 in real time and converts it
to the mask layout data that is be projected onto the
photosensitive surface of the substrate. In this way the pattern is
projected on the substrate based on the locations measured by the
vision system 340. The pattern may be projected using a sequence of
different exposures. In some cases each exposure may form a
two-dimensional layer portion of a three-dimensional optical
interconnect structure such as a waveguide.
[0025] Accordingly, in contrast to conventional optical lithography
processes, it is not necessary to use a high precision positioning
stage with interferometric feedback to precisely align the
substrate with the lithography system since the vision system 340
is used to specify the pattern that is to be formed and its
location on the substrate. For instance, while such a positioning
stage may require an accuracy on the order of tens of nanometers,
the robotic arm or scanning stage 360 employed in the fabrication
process described above only requires an accuracy in position on
the order of millimeters or sub-millimeters. The use of the vision
system nevertheless allows the optical interconnect structure to be
precisely positioned to within an accuracy of tens of nanometers.
In this way the vision system obviates the need for a high
precision positioning stage to carefully align the substrate and
the lithography system.
[0026] The fabrication process described above is further
illustrated by the flowchart of FIG. 5. At block 510 the vision
system is used to determine the precise position of the chips to be
connected and their associated connecting points at which
interconnects are to be formed. The information obtained from the
vision system is sent to the control system 350, which at block 520
employs algorithms to calculate a favorable geometry for the
waveguide interconnect structures which satisfies a number of
predetermined parameters. For example, a geometry may be selected
for an interconnect structure that permits single-mode operation
with the lowest possible propagation losses. This geometry is
converted to a digital dataset (the mask layout data) and is used
by the control system to control operation of the light source, the
programmable SLM and the scanning stage or robotic arm. In this
way, at block 530 the optical waveguide interconnect structures can
be printed in the volume of the photosensitive polymer located on
the surface of the substrate in accordance with the dataset.
[0027] The dimensions of the optical interconnect structures can be
taken from a predetermined library of dimensions or they can be
optimized in real time by minimizing the optical loss of a set of
designs using, for instance, finite-difference time-domain (FDTD)
analysis. When more than one optical interconnect structure is to
be fabricated, the locations of all of the connections are
determined to avoid overlap. Once the dimensions and trajectories
of the optical interconnect structures are determined, the exposure
dosage also can be determined by the control system based on such
factors as temperature, polymer shrinkage and humidity.
[0028] The vision system also may be used during the fabrication
process to monitor the printing of the pattern and the data so
obtained may be used by the control system in a closed-loop process
to adjust the programming of the SLM as necessary while printing is
in progress. For instance, the vision system can be used to monitor
the fidelity, contrast and size of the pattern used to form the
optical interconnect structures, as well as the exposure pattern
and dosage. The exposure pattern and dose can be changed in real
time to achieve predefine targets. Likewise, after fabrication of
all or parts of the optical interconnect structures, the results
can be examined by the vision system to look for defects. One or
more of the optical interconnect structures can be removed by wet
and/or dry etching if any defects are found and then re-printed. If
multiple exposures are employed, after a portion of an optical
interconnection is formed by one exposure the vision system may be
used to detect any defects in that exposure step before proceeding
to the next exposure step.
[0029] The process described above can be generalized to a "smart",
or adaptive, lithography operation. Whereas lithography is
understood to be the printing of a prescribed pattern, the system
described above is not limited to printing a pre-determined or
prescribed pattern. Instead, it uses an automatic adaptive
algorithm to generate a distinctive pattern in response to what the
vision system sees in its field of view. Whereas some conventional
lithography systems may have some capabilities for automatic
alignment to known reference marks in the field, they are
nevertheless still printing a pre-determined or prescribed pattern
translated to align to suitable reference marks.
[0030] In one aspect, the system described here is distinctive in
that the pattern that is printed may have altogether different
features depending on what the vision system sees in its field.
While this may also be used for alignment, the pattern that is
generated by the algorithm may differ substantially in geometry and
features beyond lateral shifts associated with alignment. The
waveguide pattern required to complete the optical connections in
an array as described earlier is just one example of such a "smart"
or adaptive lithography operation. Other examples could include, by
way of example, changes in the exposure parameters, the dimensions
or scale of features to be printed, or even radically different
patterns depending in some causal manner on what the vision system
sees. In this respect, the "smart" lithography system may find
compelling printing applications ranging from industrial
manufacturing to structures, potentially including tissues, for
biomedical and life sciences applications.
[0031] While the lithographic system described above employs an
optical lithography technique, other lithographic techniques may be
instead, such as imprint lithography or electron beam lithography,
for example. Moreover, in another alternative embodiment, instead
of fabricating the optical interconnect structures using a
lithographic process, the optical interconnect structures may be
formed using a high resolution three-dimensional (3D) printer. Such
printers are commercially available which have a resolution of 1
micron, a mechanical precision of 100 nm, an accuracy of 500 nm and
a build volume of 6.times.6.times.6 inches.
[0032] Yet another fabrication technique that may be used to form
the optical interconnect structures employs write-beams that are
injected into photosensitive material using diffractive couplers
that are integrated on the chips that are being interconnected.
This is illustrated in FIG. 6, which shows a simplified plan view
of a PIC 400 similar to that shown in FIG. 2a. As shown, two chips
410 and 420 are located on a substrate 430 and include respective
waveguides 412 and 422 that are to be interconnected with one
another. As in FIG. 2a, the waveguides 412 and 422 include inverse
tapers. Diffractive couplers 440 and 450 such as optical gratings
are respectively integrated with the respective waveguides 412 and
422. The diffractive couplers 440 and 450 are designed to couple
optical wavelengths that are out-of-band with respect to the
optical wavelengths that propagate in the waveguides 412 and 422.
Light at these out-of-band wavelengths that is launched into the
diffractive couplers 440 and 450 from a direction out of the plane
in which the PIC and waveguides 212 and 222 extend serve as write
beams that are redirected into the plane as indicated by the arrows
445 and 455 in FIG. 6. In this way the write beams 445 and 455 are
directed into the photosensitive volume of material. The
out-of-band wavelengths are chosen to induce polymerization or
other reactions that create the refractive index changes in the
photosensitive material. Interference that arises between the two
write beams causes the optical interconnect structure to be written
in the photosensitive volume of material. In this way the optical
interconnect structure is effectively "self-writing" and
"self-aligning."
[0033] While exemplary embodiments and particular applications of
this invention have been shown and described, it is apparent that
many other modifications and applications of this invention are
possible without departing from the inventive concepts herein
disclosed. For example, in some embodiments, instead of a
lithographic technique, a direct laser writing technique may be
employed in which a scanning laser is used to write the optical
interconnect structure in the photosensitive material. In addition,
in some embodiments the lithographic technique described above in
which a vision system is employed may be used to fabricate other
types of structures and devices in a photosensitive or other
material. Examples of such structures or devices include, without
limitation, integrated circuits, microelectromechanical systems
(MEMS), optical filters, microfluidic sensors, microchemical
reactors, memory devices, photodetectors, solar cells, displays and
touch sensors.
* * * * *